Sign in
Please select an account to continue using cracku.in
↓ →
Join Our JEE Preparation Group
Prep with like-minded aspirants; Get access to free daily tests and study material.
Let the locus of the centre $$(\alpha, \beta)$$, $$\beta > 0$$, of the circle which touches the circle $$x^2 + (y - 1)^2 = 1$$ externally and also touches the $$x$$-axis be $$L$$. Then the area bounded by $$L$$ and the line $$y = 4$$ is
We need to find the area bounded by the locus $$ L $$ of the centre $$ (\alpha, \beta) $$ (with $$ \beta > 0 $$) of a circle that touches $$ x^2 + (y-1)^2 = 1 $$ externally and also touches the $$ x $$-axis, and the line $$ y = 4 $$.
Let the moving circle have centre $$ (\alpha, \beta) $$ and radius $$ r $$. Since it touches the $$ x $$-axis:
$$r = \beta \quad (\text{since } \beta > 0)$$
Since it touches the circle $$ x^2 + (y-1)^2 = 1 $$ (centre $$ (0, 1) $$, radius 1) externally:
$$\sqrt{\alpha^2 + (\beta - 1)^2} = r + 1 = \beta + 1$$
Squaring both sides:
$$\alpha^2 + (\beta - 1)^2 = (\beta + 1)^2$$
$$\alpha^2 + \beta^2 - 2\beta + 1 = \beta^2 + 2\beta + 1$$
$$\alpha^2 = 4\beta$$
Replacing $$ \alpha $$ with $$ x $$ and $$ \beta $$ with $$ y $$, the locus $$ L $$ is:
$$x^2 = 4y$$
This is an upward-opening parabola with vertex at the origin.
When $$ y = 4 $$: $$ x^2 = 16 $$, so $$ x = \pm 4 $$.
The area between the parabola and the line $$ y = 4 $$ is:
$$A = \int_{-4}^{4} \left(4 - \frac{x^2}{4}\right) dx = 2\int_{0}^{4} \left(4 - \frac{x^2}{4}\right) dx$$
$$= 2\left[4x - \frac{x^3}{12}\right]_0^4 = 2\left(16 - \frac{64}{12}\right) = 2\left(16 - \frac{16}{3}\right)$$
$$= 2 \cdot \frac{48 - 16}{3} = 2 \cdot \frac{32}{3} = \frac{64}{3}$$
The area bounded by $$ L $$ and the line $$ y = 4 $$ is $$ \dfrac{64}{3} $$, which corresponds to Option C.
Create a FREE account and get:
Predict your JEE Main percentile, rank & performance in seconds
Educational materials for JEE preparation
Ask our AI anything
AI can make mistakes. Please verify important information.
AI can make mistakes. Please verify important information.